This invention relates to the analysis of maintenance procedures for complex machinery such as gas turbine engines and, more particularly, to predicting maintenance procedures and to comparing alternative maintenance procedures.
Aircraft engines and other complex, safety-critical machines are inspected and repaired on a routine basis. A routine inspection occurs at a preselected point, such as after a preselected number of flight hours or flight cycles in the case of the aircraft engine. At these points, the machine is taken out of service, disassembled as necessary, inspected as necessary, and repaired as necessary. This process is collectively termed a maintenance procedure.
In some cases, the repair of each component performed during the maintenance procedure may include any one of several workscopes. For example, the component may require only a light cleaning. It may instead require a more major repair, or in extreme cases the component may be scrapped and replaced by a new version of the same component. Gradations in these repairs may also be identified. In an aircraft gas turbine engine, for example, the turbine vanes are expensive and are subjected to extremely aggressive environments during service. Upon disassembly of the engine, the turbine vanes are inspected. Depending upon its individual condition, each turbine vane is cleaned only, repaired by welding, recoating, or other process, or replaced if the turbine vane is too damaged to be readily repaired. Each of the workscopes have associated labor requirements, supplies requirements, and financial implications.
The maintenance procedure for each gas turbine engine is typically performed many times over the life of the gas turbine engine, necessitating multiple shop visits for the engine. While the decisions as to what repairs are performed on each component at each shop visit are made primarily on the basis of technical criteria, there is a need for an approach that will allow owners and maintenance facilities to predict the labor and supplies requirements as well as the financial implications for each engine or other complex machine at each shop visit, as well as for an entire fleet of engines or other machines. The present invention fulfills this need, and further provides related advantages.
The present invention provides an approach for analyzing maintenance procedures for an article such as a component of a gas turbine engine, and for entire fleets of engines with those components (i.e., the same components present on each engine of the fleet of engine). The approach allows samples of the maintenance data to be used to predict entire maintenance procedures as well as the labor requirements, supply requirements, and financial implications. Further, this approach allows alternative maintenance procedures to be comparatively evaluated. The preferred embodiment deals with the analysis of maintenance procedures for aircraft gas turbine engines, but the present approach is equally applicable to other articles.
A method for analyzing maintenance procedures for an article such as a component of a gas turbine engine comprises the steps of providing the article, defining a set of workscopes that may be performed upon the article, and gathering maintenance frequency information for each type of subsequent trailing workscope that may be performed after a prior leading workscope, for a sample set of maintenance procedures. A measured sample workscope mix in the form of a set of trailing workscope probabilities is determined as a function of each leading workscope, using the maintenance frequency information from the step of gathering. The method further includes projecting a projected workscope mix for a set of maintenance procedures from the measured sample workscope mix. To verify the approach, a measured workscope mix may be determined and compared with the projected workscope mix.
In one application of the method, there is established a labor requirement, a supplies requirement, and/or a monetary value for each workscope. A respective labor requirement, supplies requirement, and/or monetary value for the projected workscope mix is thereafter calculated from the labor requirement for each workscope and the projected workscope mix. The labor requirement, supplies requirement, and/or monetary value (cost or price) for an entire set of maintenance procedures may thus be estimated from a sampling of the maintenance procedures.
In another application, the method further includes defining a second set of second workscopes for the article, and second gathering second maintenance frequency information for each type of subsequent second trailing workscope that may be performed after a second leading workscope, for a second sample set of maintenance procedures. The method further includes second determining a second measured sample workscope mix in the form of a set of second trailing workscope probabilities as a function of each second leading workscope, using the second maintenance frequency information from the step of second gathering, and second projecting a second projected workscope mix for a second set of second maintenance procedures from the second measured sample workscope mix. The (original) projected workscope mix and the second projected workscope mix are compared, typically as to labor requirements, supplies requirements, and/or monetary value. This approach allows different repair strategies to be compared over the entire set of maintenance procedures. Thus, for example, while a repair modification may produce a lower per-repair cost, evaluation by the present approach may show that the repair modification may result in greater repair costs when evaluated over the entire set of maintenance procedures and multiple shop visits.
In yet another application, these principles may be extended to an entire fleet of articles by providing maintenance status information for the fleet of articles, and projecting a projected fleet workscope mix for a set of maintenance procedures from the measured sample workscope mix and the maintenance status information.
Further, the results for any one component may be combined with those for other components of the engine or other machine, so that the totality of maintenance requirements may be evaluated for a single engine or the entire fleet of engines.
The present approach builds a statistical picture of the effects of alternative maintenance procedures (i.e., the leading workscopes) by assessing the frequencies of the subsequently required maintenance procedures (i.e., the trailing workscopes). The statistical picture allows the maintenance facility to plan its labor and supplies requirements, inventories, and the like. It also allows various alternative approaches to be evaluated. In an extreme example that illustrates the potential of this approach, if a first repair is inexpensive to apply in a first shop visit but results in a requirement that the component be scrapped in the next shop visit, it may be preferable to utilize a second repair that is slightly more expensive than the first repair but has a low scrap replacement level in the next repair. The present approach allows more sophisticated probabilistic judgments of this type to be made based on limited empirical data.
This technique is useful for both the owner of the engine and the provider of the maintenance services. The owner is able to project costs of ownership of the engine over time and cash flow, according to various maintenance requirements and workscope strategies. The provider of the maintenance services is able to project costs of providing services, to schedule labor and inventory of supplies for the maintenance services, and to evaluate alternative approaches to providing the maintenance services (i.e., the effect of introducing alternative workscopes). The present approach is also useful as a predictive tool. For example, if a new workscope were developed that successfully reduced the number of scrap replacements by a reconditioning process, an important question is when should the new workscope first be introduced. The present approach may show that introduction of the new workscope is not economically justified until after a certain number of shop visits have been experienced, and the full development and qualification may be scheduled with that information in mind.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.